Failed to migrate service plan of this subscription.
Failed to create hosting plan 'my Plan'
Plesk error : Template with name my Plan already exists
On the source server there is a service plan "my Plan" and on the destination server there is a service plan "my plan". So the name of plans is the same on source and target servers, but contains upper-case letters on one server only.
This is a Plesk bug PMT-1218 that will be fixed in future product updates (Reseller's, customer's logins, service plan's names and some another business objects are treated case-sensitive).
Login to the destination server via SSH/RDP.
Note: The commands below are identical for Linux and Windows.
Create backup of psa database:
# plesk db dump psa > psa.sql
Rename service plan on the destination server so that it is spelled exactly as on the source server:
# plesk db "update Templates set name='my Plan' where name='my plan'"